As is known in the art, combat identification (or CID), is the process of attaining an accurate characterization of targeted and detected objects in a battlespace. Depending upon the situation, such a characterization may be limited to identification of an object with an identifier such as “friend,” “enemy,” or “neutral.” In other situations, other characterizations may be required, including, but not limited to, class, type, nationality, and mission configuration may be used along with appropriate identifiers.
As is also known, such identification processes are sometimes carried out via combat identification systems at milli-meter wave (mmW) frequencies. Such combat identification systems typically use an interrogator antenna system which includes a directive antenna made up of an array of antenna elements. Such interrogator antenna systems are relatively large and heavy and thus are not generally appropriate for use on relatively light weaponry such as that which may be carried by a soldier. As a result, these combat identification systems are typically deployed on tanks and other large vehicular weapons platforms that can support this rather large and heavy equipment.
Attempts at extending combat identification technology to lighter weaponry (e.g. lighter than tanks and motorized vehicles) has centered upon reducing the size and weight of the large interrogator antenna arrays. One common approach to reducing the size and weight of the interrogator antenna has been to reduce the number of antenna elements which make up the directive antenna array. One problem with this approach is that by reducing the number of antenna elements in an array, the electrical aperture dimensions of the array antenna are correspondingly reduced in size. This, in turn, leads to larger azimuth discrimination angles which are not conducive to specific object targeting.
Size and weight restrictions on interrogator systems become even more of a concern in airborne applications. Furthermore, for airborne applications, additional implementation constraints such as mounting placement, aircraft weight and balance, and other related aerodynamic concerns need attention. Size, and weight must all be kept small so as not to create too much of an unwanted payload. In some applications, the airborne interrogator system must fit into an external aircraft pod of given dimensions with limited space provisions. It is also expected that operational range of airborne interrogator systems be commensurate with that achieved by ground based combat ID systems. One conventional antenna array used for ground applications is a multi-element continuous transverse stub array which has approximately a frontal area of 7 in by 4½ in or 31½ square inches (in2). For the airborne applications, a frontal aperture which is significantly smaller than that used in ground applications may be used. Therefore, to extend combat identification to a multiplicity of applications, a reduction in the size and weight of existing state-of-the-art implementations is needed. For light weaponry and airborne applications, small aperture, directive, light weight, and small physical size combat ID systems are desirable.